In power-actuated hydraulic vehicle braking systems, pedal travel simulators make a pedal travel (a lever travel in the case of a parking brake) possible upon actuation of a main brake cylinder. In the case of a power actuation, the main brake cylinder is used as a setpoint generator for a hydraulic brake pressure which is not generated with the aid of the main brake cylinder, but with the aid of external energy, for example with the aid of a hydraulic pump. The main brake cylinder is hydraulically separated from the vehicle braking system in the case of a power brake application, for example by closing a valve, and displaces brake fluid into the pedal travel simulator upon actuation.
A pedal travel simulator usually includes a cylinder and a piston, which is displaceable within the cylinder, as well as a piston spring which acts upon the piston against a displacement direction. In the case of a power actuation of a vehicle braking system, the pedal travel simulator is hydraulically connected to a main brake cylinder which displaces brake fluid into the cylinder of the pedal travel simulator upon actuation, whereby the piston is displaced in the cylinder against a spring force of the piston spring. Here, a spring rate of the piston spring, i.e. a spring force as a function of a deflection of the piston spring, essentially determines a pedal characteristic, i.e., an actuating force as a function of an actuating path of the main brake cylinder. The pedal travel simulator may always be hydraulically connected to the main brake cylinder or become hydraulically connected to and disconnected from the main brake cylinder by opening and closing a simulator valve. The deflection of the piston spring is the elastic deformation of same due to the displacement of the piston in the cylinder which results in a spring force or a change in a spring force used by the piston spring to act upon the piston against the displacement.